
■0 






DEPARTMENT OF COMMERCE 



Technologic Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON. Director 



No. 147 

AN apparatus for MEASURING THE RELATIVE 
WEAR OF SOLE LEATHERS, AND THE RESULTS 
OBTAINED WITH LEATHER FROM DIF- 
FERENT PARTS OF A HIDE 



BY 



R. W. HART, Assistant Physicist 

R. C. BOWKER, Assistant Mechanical Engineer 

Bureau of Standards 



ISSUED NOVEMBER 22.1919 



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PRICE, 5 CENTS 



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GOVERNMENT PRINTING OFFICE 

1919 



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AN APPARATUS FOR MEASURING THE RELATIVE 
WEAR OF SOLE LEATHERS, AND THE RESULTS OB- 
TAINED WITH LEATHER FROM DIFFERENT PARTS 
OF A HIDE 

By R. W. Hart and R. C. Bowker 



CONTENTS 

Page 

I. Introduction ^ 

II. Wearing-test machines 3 

III. Methods ^ 

IV. Results of tests ^ 

V. Conclusions 

I. INTRODUCTION 

The quality of sole leather is affected by many factors, such 
as the breed of the animal, its mode of life, the time of killing, 
the method of preserving the hide, and the kind of tannage. A 
very important factor which influences the durability of any 
particular sole is the part of the hide from which it is cut. It is 
a difficult problem to measm-e the wear of sole leather and gen- 
erally it is accomplished by actual service tests on individuals. 
Such a method takes considerable time, and the value of the 
results obtained is often uncertain on account of the many imcon- 
trollable variables occurring in the types of service and among 
the individuals \\ earing the soles. The development of a simple 
method for quickly determining the durability of sole leather 
seemed desirable, and this paper discusses a laboratory apparatus 
designed for this purpose and also presents the results of tests 
made to date to determine the relative wear of leather from 
different parts of a hide. 

n. WEARING-TEST MACHINE 

A machine has been developed at the Bureau for testing the 
durability of sole leather with the idea of subjecting the leather 
to shearing action during the wear similar to that occurring in 
service on shoes and at the same time accelerating the actual 
wearing away of the material so that an indication of the dura- 
bility of the specimen might be obtained in about 24 hours. The 

137325°— 19 3 



4 Technologic Papers of the Bureau of Standards 

machine as first designed (Fig. i) embodied a cam of clover-leaf 
shape, to which the samples were attached, and which rested on 
a horizontal disk having an abrasive smiace of cement. The 
difficulties with this design were that the samples were submitted 
to a bumping action which caused the wear of each sample to be 
so localized that it was often worn through on one end before 
the other end showed appreciable wear, that no means was pro- 
vided for removing the material worn away, and that the abrasive 
material soon wore smooth which caused a longer time to be 
necessary for a test. The machine (Fig. 2) as later developed 
and as now used is described as follows: 

A wheel of 15 -inch diameter carries on its face 12 test pieces. 
The wheel revolves at the rate of 30 revolutions per minute about 
a horizontal, axis with its bearings in two parallel metal bars 
which are pivoted at one end, the other end being free. The wheel 
carrying the weight of the bars (and any additional weight that 
may be suspended from their free ends) , rests on a horizontal disk 
of 16-inch diameter, the point of contact being ^}4 inches from 
the axis of the disk. This disk has a surface of carborundum, and 
rotates about a vertical axis on which is a brake wheel provided 
with a brake strap, by means of which any desired resistance to 
rotation may be secured by the application of dead-weight. The 
wheel is driven by a chain and in turn drives the horizontal disk 
with which the test pieces are in contact. The apparatus is 
designed with the view of subjecting the test piece to (i) a driving 
(shearing) action tmder pressure, and (2) a slight abrasive action 
resulting from the circular path of contact between the wheel and 
disk. The conditions of pressure and shear may be adjusted as 
desired. A circular brush is shown resting on the carborundum 
disk. This brush in connection with a small exhauster tends to 
keep the surface of the wearing disk clean. 

A test usually consists of 40 000 revolutions of the wheel which 
corresponds with 40 000 steps, or approximately 40 miles of walking. 

The substitution of a wheel for the cam eliminated the bimiping 
action but retained the shearing action and resulted in a more 
even and smoother operation. The use of a wheel allowed more 
specimens to be tested at one time, the entire surfaces of which 
were subjected to the wearing action. By using carborundum for 
an abrasive, a material was obtained which did not become dull 
or smooth quickly and which could be resm-faced with an emery- 
wheel dresser. 



Bureau of Standards Technologic Paper No. 147 




P"iG. I. — Wearing test machine as fust used 




Fig. 2. — Wearing test viachine as used at present 



Jureau of Standards Technologic Paper No. 147 



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pjQ_ 2. — A 6e%c^ marked off for machine wearing test 



Wear Resistance of Sole Leather 5 

A small suction fan and circular brush were added to the equip- 
ment in order to remove the dust caused by abrasion. These 
improvements permitted the wearing conditions to be more uni- 
formly maintained, 

m. METHODS 

Sole leather is generally sold in the form of bends. A bend is a 
half of a hide with the shoulder and belly portions trimmed off, 
the remaining portion being suitable for soles. In the tests con- 
ducted samples of leather from different locations on a bend were 
used to determine their relative durability or resistance to wear. 
When a whole bend was tested the general scheme was to divide 
it into blocks, as illustrated in Fig. 3. Each block was stamped 
with a code number, which fixed its location on the bend. When 
using the clover-leaf-shaped cam for holding the samples, test 
pieces approximately 24 by 5 cm were required and they were 
attached to the cam by a clinching device. Test pieces for use 
with the wheel were about half as long and were attached by 
means of four countersunk screws. In either case the samples 
were first weighed and then placed on the machine. After the 
test was completed the samples were again weighed and the loss 
in weight determined. The relative durability was obtained by 
determining the loss in volume from the loss in weight and the 
specific gravity. The sample showing the greatest loss in volume 
was considered as the least durable. 

A small sample adjacent to the test specimen was used in de- 
termining the specific gravity. Since only the grain portion was 
worn away during the test, it was thought desirable to use the 
specific gravity value for the grain portion only. Accordingly 
the flesh portion of the sample was removed and the grain portion 
was then coated with cellulose nitrate to render the sample water- 
proof. The determinations were then made using a direct-reading 
gravitometer (Fig. 4). 

IV. RESULTS OF TESTS 

Test No. I. — This series of tests was conducted on an oak-tanned 
bend using the machine with the clover-shaped cam to carry the 
samples and an abrasive disk of cement. The length of the test 
was 40 000 revolutions except that in some cases one of the test 
pieces was entirely worn through before the 40000 mark was 
reached; in these cases the machine was stopped and the results 
figured on a proportional basis. 



6 Technologic Papers of the Bureau of Standards 

The foiir pieces tested at the same time were all taken from the 
same colimm across the bend and equidistant from each other so 
that each nm gave an indication of the relative wear across the 
bend. The exact location of each test piece is shown in Fig. 3. 

The results show that in general the resistance to wear is greater 
at the backbone edge and decreases gradually toward the belly 
edge of the bend. This is shown in Fig. 5. In studying these 
results it should be remembered that the best wearing portions of 
the bend are represented by the lowest points on the ciirves. In 




Fig 4. — Direct reading gravitometer 

diagrams B, C, and D the results of each individual run may be 
distinctly seen as one continuous curve, and the general tendency 
in regard to the wear as stated above is shown in each case. In 
diagram A , all the points in the other three diagrams are plotted, 
which gives a broken curve, showing that tests of practically the 
same material made at different times did not check. This failure 
of the machine to check itself caused the changes previously 
discussed to be made. 

Test No. 2. — A scoured oak bend was used in this series of tests. 
The samples in this case were 10 by 5 cm. in size, and when placed 




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137326°— 19. (TofacopascO.) 



Fig. 5. — Results of test No. i (ordinales indicate loss in ieear'"9 '"'^' 



Wear Resistance of Sole Leather 7 

on the wheel were made to an apparent even thickness by backing 
the thinner ones with sheets of metal so that the outer circumfer- 
ence of the wheel, after all the test pieces were in place, presented 
a smooth surface. Twelve pieces were tested at one time. The 
same general scheme of placing the samples on the machine for 
this test was carried out as in Test No. i. 

The results of the tests are given in Fig. 6 and show that the 
best wearing portions of the bend are along the backbone edge and 




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Fig. 6. — Results of test No. 2 (ordinates indicate loss in wearing tests) 

over the kidney. The resistance to wear decreases as the belly 
edge is approached and also toward the shoulder end of the bend. 
Test No. 3. — Test No. 3 differs from the preceding test mainly 
in the fact that the leather was of hemlock tannage instead of oak 
tannage, and that the conditions of pressure and shear were chang- 
ed, so that no comparison can be made between the relative wear 
of the oak and hemlock tannages. The tests were made along the 
bend with samples of composition material placed alternately on 
the machine with the leather. The general tendency of the de- 
creasing resistance to wear as the belly edge and the shoulder end 



Technologic Papers of the Bureau of Standards 







Wear Rssistance of Sole Leather 9 

are approached is shown in Fig. 7. This test also shows that the 
portion on the extreme butt end near the tail is inferior in wearing 
quality. 



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23 


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34 


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16 


35 


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Fig. 8. — Method of dividing a bend for service and machine tests 



Test No. 4. — Several bends of sole leather were divided into 
blocks as shown in Fig. 8. From each block a sole was cut which 
was used in an actual service test. A sample for the wearing-test 




11 13 13 



15 21 82 
Location 



23 24 25 31 

on the Hide 



Fig. g.-Chart showing relation between actual service tests and laboratory machine tests 

in test No. 4 

machine was also secured from each block adjacent to the toe end 
of the sole. A comparison of the results obtained in service and 
on the machine is shown in Fig. 9. 



lO 



Technologic Papers of the Bureau of Standards 



The upper curve represents the average wear in days per iron^ 
for all the soles from each location. The lower curve represents 
the wear as indicated by the machine tests expressed as the average 
loss in volume of the test pieces as compared with a standard speci- 
men of composition material, a sample of which was tested with 
each group of six samples of leather. The two curves show the 
same general tendency as regards wearing quality with the excep- 
tion of location No. 3 1 , No cause can be assigned for this apparent 
discrepancy, but it is expected that subsequent investigations will 
correct this difference. 

V. CONCLUSIONS 

The results of these tests show that the machine indicates a 
decided difference in the wearing quality of leather taken from 
different parts of the hide, the portion near the back and over the 
kidneys having the best wearing quality and those portions near 
the belly edge, shoulder end, and extreme butt end having con- 
siderable less durability. These indications are in accord with the 
opinion and experience of many tanners and leather manufactiurers. 
The results obtained on the machine in Test No. 4 also agree quite 
closely with those obtained in service tests. 

In view of these facts it seems reasonable to believe that the ma- 
chine may properly be used to indicate the relative resistance to 
wear of different leathers. 



Washington, May 26, 191 9. 



1 The iron is a unit of measure used in the leather trade to designate the thickness or gage of leather and is 
equal to approximately one-half millimeter in the metric scale, and equal to one forty-eighth inch in the 
EngUsh scale. 



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